A control device for an internal combustion engine is disclosed in Patent Document 1. The internal combustion engine disclosed in Patent Document 1 includes a supercharger and an exhaust gas recirculation device.
The supercharger is used to increase a pressure (hereinafter, this pressure is referred to as a “supercharging pressure”) of a gas suctioned into a combustion chamber, and includes a compressor which is disposed in an intake passage, an exhaust turbine which is disposed in an exhaust passage, and a vane which increases or decreases a pressure (hereinafter, this pressure is referred to as an “exhaust pressure”) of an exhaust gas inside the exhaust passage at the upstream side of the exhaust turbine. Further, when the exhaust pressure is increased by changing the operation state of the vane (more specifically, by decreasing the opening degree of the vane), the rotation speed of the exhaust turbine increases. Accordingly, the rotation speed of the compressor also increases, and thereby the supercharging pressure increases. Meanwhile, when the exhaust pressure is decreased by changing the operation state of the vane (more specifically, by increasing the opening degree of the vane), the rotation speed of the exhaust turbine decreases. Accordingly, the rotation speed of the compressor also decreases, and thereby the supercharging pressure decreases.
Further, the exhaust gas recirculation device (hereinafter, this device is referred to as an “EGR device”) is used to introduce the exhaust gas into the combustion chamber by introducing the exhaust gas, discharged from the combustion chamber to the exhaust passage, into the intake passage, and includes a passage (hereinafter, this passage is referred to as an “EGR passage”) extending from the exhaust passage at the upstream side of the exhaust turbine to the intake passage at the downstream side of the compressor and a control valve (hereinafter, this control valve is referred to as an “EGR control valve”) which controls the flow rate of the exhaust gas flowing inside the passage. Further, when the flow rate of the exhaust gas flowing inside the EGR passage is increased by changing the operation state of the EGR control valve (more specifically, by increasing the opening degree of the EGR control valve), an amount (hereinafter, this amount is referred to as an “EGR gas amount”) of the exhaust gas introduced into the intake passage increases, so that a ratio (hereinafter, this ratio is referred to as an “EGR ratio”) of the EGR gas amount in the gas suctioned into the combustion chamber increases. Meanwhile, when the flow rate of the exhaust gas flowing inside the EGR passage is decreased by changing the operation state of the EGR control valve (more specifically, by decreasing the opening degree of the EGR control valve), the EGR gas amount decreases, so that the EGR ratio decreases.
Here, when the exhaust pressure is increased by changing the operation state of the vane, a difference between the exhaust pressure and the supercharging pressure increases, and the EGR gas amount increases, so that the EGR ratio increases. Meanwhile, when the exhaust pressure is decreased by changing the operation state of the vane, a difference between the exhaust pressure and the supercharging pressure decreases, and the EGR gas amount decreases, so that the EGR ratio decreases. In this way, when the operation state of the vane is changed so as to change the supercharging pressure, not only the supercharging pressure but also the EGR ratio change.
Meanwhile, when the EGR gas amount is increased by changing the operation state of the EGR control valve, the exhaust pressure decreases, and hence the supercharging pressure decreases. Meanwhile, when the EGR gas amount is decreased by changing the operation state of the EGR control valve, the exhaust pressure increases, and hence the supercharging pressure increases. In this way, when the operation state of the EGR control valve is changed so as to change the EGR gas amount, not only the EGR gas amount but also the supercharging pressure change.
Further, in this way, the change in the operation state of the vane influences not only the supercharging pressure but also the EGR gas amount and the change in the operation state of the EGR control valve influences not only the EGR gas amount but also the supercharging pressure. Accordingly, in the control device disclosed in Patent Document 1, when the operation amounts to be input to the vane and the EGR control valve are determined so as to change the operation state of the vane and the operation state of the EGR control valve so that the supercharging pressure and the EGR ratio are respectively controlled at the target supercharging pressure and the target EGR ratio, the aforementioned operation amounts are determined in consideration of the influence on the EGR gas amount due to the change in the operation state of the vane when the operation state of the vane is changed and the influence on the supercharging pressure due to the change in the operation state of the EGR control valve when the operation state of the EGR control valve is changed.
That is, the operation amounts to be input to the vane and the EGR control valve are determined by the cooperation of the control of the supercharging pressure due to the control of the operation state of the vane and the control of the EGR ratio due to the control of the operation state of the EGR control valve.